FEELING AND TOUCH. 399 



seem to feel it long after we have let it go. This is a kind 

 of echo of sensation, and is purely subjective. 



The manner and form in which the sensation of pressure 

 is produced by different bodies give us such exact informa- 

 tion as to their nature, that we might, without close examina- 

 tion, suppose this to be the result of special sensations. Thus, 

 we judge if the surface of a body is smooth or rough, if it 

 exhibits any anfractuosity (peculiar conformations), by the 

 way in which it presses upon our digital extremities ; by 

 passing our fingers over surfaces we judge of their form. The 

 variations of pressure, and the reactions of a body in opposi- 

 tion to efforts which we ourselves make, enable us to judge 

 whether it is hard or soft: we judge in the same way whether 

 it is in large pieces or dust ; whether it is solid or liquid : in. 

 short, we obtain precise ideas as to the condition, the form, 

 and extent of the body. 



Differences of pressure also enable us to judge of the weight 

 of a body ; but it must be admitted that the muscular force 

 necessary to counterbalance the weight (see p. 453) is of 

 chief importance in our estimate. 



Finally, the sensations of pressure, form, weight, and tem- 

 perature, are often connected with each other ; thus, of two 

 equal weights, the colder will seem the heavier ; if we place 

 upon our forehead two five-franc pieces of different temper- 

 ature, the warmer will appear to be the lighter. On the 

 other hand, smooth bodies appear to be colder than those of 

 uneven surface, and, subjectively, they really are so, because, 

 their surfaces being unbroken, more caloric is drawn from us. 



The most striking example of the perfection to which the 

 sense of touch may be brought, is found in the case of blind 

 persons, who learn to distinguish colors by touch ; as they 

 do this solely by means of the different degrees of roughness, 

 they are unable to distinguish natural colors whose surface 

 is equally smooth. 



Finally, the sensations, whether general or special, pro- 

 duced by the skin, are reduced to three : contact (or pres- 

 sure), temperature, and pain. The nature of these three 

 kinds of sensations, and the manner in which they are pro- 

 duced, are as yet undecided ; as loss of sensation to one may 

 exist, while sensation to the others remains intact, we are led 

 to suppose that a separate class of nerve fibres belongs to 

 each, and that pain, for instance, has not the same path of 

 conduction as sensations of touch, while the latter follow 

 other conductors than those of the sensations of temperature. 



